Contacting element



Patented Dec. 5, 3939 warren stirs P'TFET FEC CONTACTING ELEMENT NoDrag. Application awn 15, 1939, Serial No. 268,119

7 Claims.

This invention relates to electrical contactin members.

It is an object of the invention to provide an improved circuit makingand breaking contact that has a substantial current carrying capacity,as well as a relatively low and uniform contact resistance throughout along period of circuit interrupting service.

It is also an object of this invention to provide a contact materialwhich will be highly resistant to sticking or welding.

It is a further object of this invention to provide a contact memberwhich is resistant to mechanical wear and to material transfer.

Other objects of the invention will be apparent from the followingdescription taken in connection with the appended claims.

The present invention comprises the combination of elements, methods ofmanufacture and the product thereof, brought out and exemplified in thedisclosure hereinafter set forth, the scope of the invention beingindicated in the appended claims.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the combination of elements, without departing from thespirit of the invention.

The contacts may be composed of copper and metallic thalliumaccordingly. The ingredients may be present in approximately thefollowing proportions:

Per cent Thallium .05 to 20 Copper Predominantly the balance Copper andthallium are almost insoluble in each other in the solid state, andtherefore the final structure of alloys of the type described 40 in thepresent invention, show a matrix of almost pure copper with thalliumparticles imbedded therein, in a more or less uniform manner. Thedistribution of the thallium particles will depend on the melting,pouring and solidifying conditions. It is also influenced by theaddition of ternary ingredients.

We have found that copper-thallium alloys of the type described in thepresent application can be made still more effective for electricalcontacting purposes, if elements are added, which are characterized bylow boiling point, and more particularly by boiling points which arebelow 1200 degrees C. Elements of that nature are cadmium, which has aboiling point of 767 degrees C., zinc, which has a boiling point of 907degrees C., selenium, which has a boiling point of 688 degrees C.,arsenic, which has a sublimation point of 615 degrees 0., calcium,having a boiling point of 1170 degrees C., mercury, having a boilingpoint of 356.9 degrees 0., sulfur, 5 having a boiling point of 444.6degrees C., magnesium having a boiling point of 1110 degrees C.

I have found that a structure in which two metals are present, whichhave entirely different melting, wetting, oxidizing and evaporating con-10 ditions, are extremely well suitable for electrical contact purposes.In many cases, it is desired to have solid solution alloys for contactpurposes.

This is primarily the case where noble metals are being used, to whichbaser materials are added. 15 If, in such alloys, base metals are takenup in solid solution, and are held within certain proportions, then theresulting alloy will have characteristics similar to those of the noblemetal. In other words, physical properties, such as oxi- 20 dationresistance and corrosion resistance, are improved by the formation of asolid solution; on the other hand, the electrical conductivity isusually considerably decreased.

The recent developments in contact materials 2 have shown that metalsofa duplex structure, and particularly metals in which a refractorymaterial is present, in combination with a lower melting point material,have given outstanding performance as far as sticking and welding char-30 acteristics are concerned. At the same time, the erosion of suchmixtures is greatly reduced as compared with that of solid solutionalloys. This can be explained by the fact that when a solid solutionalloy is used for contact materials, and 3 such solid solution alloycontains ingredients of the nature of cadmium, which will readilyevaporate, then such evaporation will destroy the solid solution andcause a breakdown of the crystal structure, resulting inincreasedelectrical wear. 4 If, on the other hand, cadmium would be present asfree cadmium and the balance of the structure would be made up of ametal not alloying with cadmium, then only the cadmium particles canevaporate, but the main structure of the ma- 45 terial is retainedundisturbed.

In the case of the present invention, the two metals which perform thecontact functions are thallium and copper, thallium being a soft metalof good corrosion resistance. Thallium forms an oxide readily. Inperforming as a contacting element in a mixture of copper and thallium,the heat created by arcing or sparking conditions, will convert theexposed thallium particles to thallium oxide, since the air will beionized between the contacts so that the oxygen becomes highly active.

Since thallium particles are uniformly dispersed between the copperparticles, .they will tend to act as a non-wetting constituent as soonas they have been converted into oxides and provide a contact materialwhich will have a much greater resistance to welding or fusing undervery severe electrical loads. For this purpose again, it -is of greatimportance that the two metals are present in their free state. Ifthallium would be taken up in solid solution by the copper, theoxidizing conditions during arcing would affect the solid solutioncrystals and the separation of metallic particles by oxide layers wouldnot be obtained.

We have found that binary copper-thallium alloys are extremely wellsuited for electrical contacts and the above reasoning seems to ofier asatisfactory explanation for this behaviour.

This reasoning, however, is at present only a theory, since there are nophysical laws or definitions which will account for thesuperiority ofour improved compositions over the alloys of the prior art. We want itto be understood, therefore, that the theory explained in the presentteaching is of a preliminary nature only and may be superseded later onby further research.

We have also found that the addition ofjlow boiling point constituentsto the present composition is highly beneficial. due to the formation ofoxides because the metal vapors will probably oxidize very readily,during arcing conditions, and more generally during the make and breakof the contact. At the same time, the actual metal vapors may have whatis usually termed as are quenching properties. 1

Some of the compositions that we have found to be particularly usefulare the following:

. Per cent (a) Copper 9'7 Thallium 3 (1 Copper... 9o Thallium 10 (c)Cadmium 2 Thallium 3 Copper 95 (d) Zinc -1 1 Thallium v 2 Copper Balance(e) Selenium .5

Thallium 3 Copper Balance (f) Sulfur .3

Thallium 3 Copper"--. Balance This may also be Per cent (g) Arsenic .75Thallium 2 Copper Balance (h) Magnesium 2 Thallium 3 Copper 95 The abovecompositions are given by way of an example, and within the scope of thepresent invention there are a number of other compositions that can beselected for specific purposes.

The alloys can be made according to standard melting procedures and canbe cast into molds. If the thallium content is low enough, these alloyscan be extruded into suitable shapes, from which, for instance,contactor contacts can be manufactured. If the contents of thallium andthe other low boiling point constituents are too high, then these copperbase alloys must be cast directly into the shape in which they are goingto be used.

While the present invention as to its objects and am; antages has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby, but it is intended to cover theinvention broadly, within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contacting element formed of a copper base alloycontaining .05% to 20% thallium.

2. An electrical contacting element composed -of an alloy containing .05to 20% thallium and the balance substantially all copper.

3. A contacting element composed of an alloy containing .1 to 10%thallium and the balance substantially all copper.

4. A contacting element composed of an alloy elements cadmium, zinc,selenium, arsenic, cal-.

cium, magnesium, mercury and sulfur.

6. A contacting element composed of a copper base alloy containing .1 to10% thallium and up to 10% of an element having a boiling point below1200 degrees C., comprising the elements cadmium, zinc, selenium,arsenic, calcium, magnesium, mercury and sulfur.

7. A contacting element composed of a copper base alloy containing 1 to5% thallium and up to 10% of an element having a boiling point below1200 degrees 0., comprising the elements cadmium, zinc, selenium,arsenic, calcium, magnesium, mercury and sulfur.

FRANZ R. HENSEL. EARL I. LARSEN.

